Various types of selective radiation transmitting and radiation blocking foils and layers have been proposed, for example to prevent the heating of interior spaces by excessive sunlight in the summertime. Such foils, for example, include a reflective coating which reflects sunlight. Heat barriers also have been proposed to increase the efficiency of interior space heating by preventing radiation towards the outside in wintertime, by decreasing the transmission of heat, and hence heat losses from the interior of a heated space towards the outside ambient air (see, for example, German Patent Disclosure Document DE-OS No. 27 03 688 and corresponding U.S. Pat. No. 4,158,718 which is hereby incorporated in its entirety).
Sunlight barriers, as well as heat barriers, operate on the principle of reflection of radiation by a metal film applied to a substrate carrier, typically a flexible foil or a glass plate. The metal film is vapor-deposited, or applied by a similar process, such as atomization of a metal. Transmissivity of light within the visible spectral range of such a thin metal layer can be increased by an anti-reflection coating. Multi-layer systems including metallic and dielectric layers, have also been proposed. The metals which are usually used as the heat reflectivity layer are silver, gold, aluminum, and copper. The dielectric materials, that is, the electrically non-conductive layers, are metal oxides of high refractive index, such as, for example, TiO.sub.2, SiO.sub.2, Ti.sub.2 O.sub.3, Ta.sub.2 O.sub.5, ZrO.sub.2, Sn oxide, bismuth oxide, indium oxide, or metal sulfides, such as for example, ZnS. Such multi-layer systems, applied to plastic foils or glass plates, are used as heat transmission barriers or to provide for a flat plane heating arrangement. Heat barriers should have a high light transmissivity within the visible spectral range, and a high reflectivity for infrared radiation, particularly of far infrared, that is, in a wave length of .lambda.=10 .mu.m approximately for heat radiation from an interior space towards the outside.